1. Field of the Invention
This application relates generally to devices and methods for non-invasively measuring the concentration of a substance in a subject's blood, and more particularly, to devices and methods for non-invasively measuring the concentration of glucose in the subject's blood.
2. Description of Related Art
Numerous systems were suggested in the last decades, to solve the problem of non-invasively measuring the level of substances (e.g., glucose) in a subject's blood. The main drawback of all those systems was a very poor signal to noise ratio, which required a very heavy computing system, and resulted in inconsistent and unrepeatable results.
In addition, conventional systems for non-invasive measurement of substances (e.g., glucose) in the blood do not take into consideration the various parameters that affect such measurements in human tissue. For example, conventional systems that utilize measurements taken from the eye do not take into consideration the changing parameters of the eye, such as pupil size, other materials of the eye, the absorption or scattering of light inside the eyeball. In particular, U.S. Pat. Nos. 6,494,576 and 5,820,557 suggest subtracting the reflected light intensity from the intensity of the originally irradiated light and to correlate this subtracted value to glucose concentration.